gce physics 8ph0 02 - revisely

Examiners’ Report

June 2018

GCE Physics 8PH0 02

Edexcel and BTEC Qualifications

Edexcel and BTEC qualifications come from Pearson, the UK’s largest awarding body. We provide a

wide range of qualifications including academic, vocational, occupational and specific programmes

for employers. For further information visit our qualifications websites at www.edexcel.com or

www.btec.co.uk.

Alternatively, you can get in touch with us using the details on our contact us page at

www.edexcel.com/contactus.

Giving you insight to inform next steps

ResultsPlus is Pearson’s free online service giving instant and detailed analysis of your students’

exam results.

See students’ scores for every exam question.

Understand how your students’ performance compares with class and national averages.

Identify potential topics, skills and types of question where students may need to develop their

learning further.

For more information on ResultsPlus, or to log in, visit www.edexcel.com/resultsplus.

Your exams officer will be able to set up your ResultsPlus account in minutes via Edexcel Online.

Pearson: helping people progress, everywhere

Pearson aspires to be the world’s leading learning company. Our aim is to help everyone progress

in their lives through education. We believe in every kind of learning, for all kinds of people,

wherever they are in the world. We’ve been involved in education for over 150 years, and by

working across 70 countries, in 100 languages, we have built an international reputation for our

commitment to high standards and raising achievement through innovation in education. Find out

more about how we can help you and your students at: www.pearson.com/uk.

June 2018

Publications Code 8PH0_02_1806_ER

All the material in this publication is copyright

© Pearson Education Ltd 2018

2 GCE Physics 8PH0 02

http://www.edexcel.com

http://www.btec.co.uk

http://www.edexcel.com/contactus

http://www.edexcel.com/resultsplus

http://www.pearson.com/uk

IntroductionThis is the third time that the Pearson Edexcel AS paper 8PH0 02, Core Physics II, has been sat by

students. Section A of the paper contains eight multiple choice questions followed by questions of

increasing length and increasing demand. This section examines the Waves and Materials

components of the course providing a transition for students between GCSE and A Level. Section B

contains two questions, with the first question taking inspiration from a short passage. This section

is designed to provide a synoptic element with responses from any part of the AS specification

expected. In this case Question 15 relied on knowledge from some aspects of dc electricity and

mechanics, whilst Question 16 required understanding of fluid mechanics. This paper enabled

students of all abilities to apply their knowledge to a variety of styles of examination questions.

Many students have shown good progression from GCSE to AS level, with prior knowledge

extended. Some questions were not answered as well by many students as would have been

expected . Full written and open response questions, in particular, fell into this category as students

struggled to explain the physics, as in Q9. students would benefit from more practice at applying

familiar ideas and concepts in an unfamiliar context in order to follow through an argument and

reach a conclusion, as in Q14(b)(iii). The recall of some basic mathematical equations such as the

volume of a sphere was not known to some.

Analysis of Multi-choice questions

Multiple-choice questions were generally well answered. The more able student typically scored at

least 7 correctly whilst an E grade student typically scored around 5 marks.

Question description Percentage of

students with

correct response

Common incorrect

responses

1 Expression for Young Modulus 87% D

2 Pulse Echo 84% A

3 Stationary waves 56% A,C

4 Photoelectric equation 78% B

5 Diffraction of electrons 60% C,D

6 Phase difference 54% B,D

7 Speed of a wave on a string 59% C,D

8 Mass per unit length of a string 70% A

GCE Physics 8PH0 02 3

karen

karen

Remove space before full stop

Question 9

This 6-mark indicative content question proved a challenge to many. Whist it was clear that this

type of the hysteresis graph was familiar to many, students struggled to describe its shape in a

coherent manner. Those who were the most successful at this question started with observations

from the graph (as the question suggested) and then used their knowledge of force-extension

graphs to explain these observations in terms of forces and in terms of energy.

Firstly recognising that this is not a straight line graph and, secondly, that the start and end points

are the same, leads to MP1 and MP2. These were the most commonly scored marks. MP3 was

awarded for a comparison between the shape of the two graphs with an explanation of the

differences when loading and unloading in terms of force and extension. MP4 was awarded for a

comparison in the area under the graphs for loading and unloading, with an explanantion in terms

of energy, for MP5. Finally, MP6 uses all of this to explain the hysteresis in terms of the transfer of

heat energy, linking back to information given in the question.


This answer scores 5 indicative marking points.

MP1 in line 2. Allowance was made for the graph

being approximately a straight line for small forces

and extensions.

MP2 last sentence.

MP3 not awarded.

MP4 in lines 3 to 4.

MP5 in lines 4 and 5.

MP6 in lines 6 to 8. "energy lost" on its own is

insufficient, but in this answer it links back to

thermal energy in line 4.

The marks awarded for these 5 incative marking

points plus the linkage marks gave a total of 5 for

the question.


Question 10 (a)

A 2-mark calculation using the equation from the back of the examination paper for elastic strain

energy.

A correct answer showing all working clearly.

A common incorrect answer.

This student has used the equation for work done

= force X distance not realising that the work done

on the spring is equal to the elastic strain energy.


Question 10 (b)

A 2-mark calculation using the Hooke's law equation as given at the back of the examination paper.

Students were expected to realise that, as the same spring is used, the spring constant remains the

same in both (a) and (b).

This student has used data from the question to

calculate a value for the spring constant of the

spring, k. This is then substituted back into the

Hooke's law equation using the new data to arrive

at a correct answer.


This student has bypassed the need to determine

a value for the spring constant by equating the

ratios of extension to force for the two situations.

Rearranging the equation they then reach a correct

value for the extension.

Be careful with units. Usually it is wise to convert

cm to m. However in this question it was not

necessary to do this as long as the correct unit for

extension was given at the end.

When calculating the force, extension should be in

SI units.


Question 11 (a)

A question assessing the student's ability to judge factors that might affect the accuracy of

measurements.

Many students indicated the need for repeats and this was one of the more common responses

seen. However, they could not score the mark if they then failed to state that a mean should be

determined.

There were many responses referring to using thin /sharp pencils which did not score a mark. Also

parallax, which did not score a mark as the protractor would have been flat on the paper and so

parallax would not have been an issue.

This student scores 2 marks - for the use of large

angles (one mark) and thin rays (second mark).

Neither of these were commonly seen.

Accuracy is an indication of how close a

measurement is to the true value


karen

karen

Insert full stop

Question 11 (b)

(b)(i) Correct use of the term resolution means that

this student could access full marks. A correct

conclusion is given to the suggestion of a

resolution of 1 degree.

(b)(ii) An attempt at a percentage uncertainty

calculation using an uncertainty of 0.5 has been

made. Unfortunately they have used an angle of 50

degrees (= i) instead of the correct 29 degrees,

(angle r when i=50 degrees). This mistake was not

uncommon.


Students would benefit from revising the glossary

in appendix 10 of the specification. Use of these

key terms can help to raise the level of a students'

written responses.

A correct answer scoring full marks.


Question 11 (c)

In part (c)(i) the line of best fit proved a challenge for many students. The line was judged by an

even spread of points lying either side of the line. The final point at sinr=0.6 could have been

treated as an anomaly and ignored.


(i) An acceptable line of best fit for this student.

They have not treated the final point as an

anomaly and have an even spread of points either

side of the line.

(ii) A gradient has been calculated, using a large

range for sini and sinr shown clearly with the

drawing of the triangle on the graph. Refractive

index is calculated correctly with a correct

conclusion.

Some students used the data points from the stem

of the question instead of calculating a gradient so

would have been unable to score MP1.

When calculating gradients use as large a range of

the x and y axes as possible but it must be at least

half the height or width of the graph. It is good

practise, and makes it clear to the examiner if the

triangle is drawn on the graph. This can also avoid

errors with calculating the change in x and the

change in y, especially when (as is the situation

here) the line does not go through the origin.


The line of best fit is sufficient for the mark. The

final point has been treated as an anomaly and

ignored. There are three points on the line and two

other points sitting equidistant either side of the

line, constituting an even spread of points. The line

has not been forced through the origin.

When drawing lines of best fit, do not force the line

through the origin.


Question 12 (a)

Students demonstrated an understanding of energy levels This has been a common theme in past

papers, but in the context of energy gained from the absorption of photons. The context in this

question, with energy gained from collisions, was clearly less familiar and this caused some

difficulties. Some students confused this with the photoelectric effect with photons absorbed and

photoelectrons emitted. Marks could not be awarded for repeating information from the question.


MP1 awarded in line 1 despite the misspelling of

discrete. However, "electrons exist in certain

energy levels" would not have been accepted as it

does not convey the same meaning.

MP2 lines 4 and 5.

MP3 line 6.

MP4 and MP5 in the last 4 lines.

This response, of over 10 lines, contains only one

sentence, making it more difficult to read.


MP1 in line 5. Since the student is referring to

electrons rather than atoms.

MP2 line 2 the idea that an electron moves down

an energy level.

MP3 line 3.

MP4 lines 4 and 5 linking energy changes to

frequency.

MP5 lines 4 to 6.

Marks are not awarded for repeating information

in the question. Use the information given but add

further detail.


Question 12 (b)

When the electron collides with the mercury atom its speed, and hence its kinetic energy, decreases

as it tranfers energy to the atom during the collision. The amount of energy transferred is equal to

the difference in the kinetic energy of the electron before and after the collision. The wavelength

emitted by the mercury atom corresponds to the total energy absorbed by the mercury atom.

As this is a "deduce" question, having calculated a value for wavelength, candidates are expected to

use the data in the table to state which type of radiation is emitted.


This is a correct 4 mark answer.

In the first 5 lines the student has correctly

calculated the kinetic energy of the electron at

each of the two speeds and then subtracted their

answers to calculate the change in energy of the

electron due to the collision.

They have then correctly calculated the frequencey

(lines 6 and 7) and the corresponding wavelength

(last line) to obtain an answer within the

accepetable range (2.37 rounds to 2.4). For the

final mark a conclusion of ultraviolet is given.


In this response the difference in the two speeds

has first been determined and then this value

substituted into the formula for kinetic energy.

This is incorrect as the value obtained is not the

change in the kinetic energy of electron. This

mistake was often seen.

However they have scored MP2 and MP4. Whilst

their final numerical answer is incorrect, and so

not achieving MP3, they have made a correct

conclusion (infrared) based upon their answer and

so can score MP4.


Question 13 (a)

A wavefront is a line or surface along which all the points on a wave are in phase. (This enables a

measurement of wavelength to be made from the distance between wavefronts).

Many students were unsure on this. They had the idea but were unable to express it concisely.

This answer gains the mark. The student did not

need to write both line and surface for the mark.

Students should memorise this.


Question 13 (b) (i)

Any idea that a laser should not be shone towards the eye.

Unqualified reference to the wearing of goggles was commonly seen but was not accepted.

Scores 1 mark.


Question 13 (b) (ii)

This question required the idea of evidence, or lack of.

Students would benefit from gaining an appreciation of the history of the development of the wave-

particle duality concept.

This scores the mark for the last alternative on the

markscheme "support for the particle model" as

they have stated that the support came from an

eminent scientist.

A significant number of students referred to

Einstain or the photoelectric effect, neither of

which were around in 1803.


An example of a response that scores for the first

alternative "lack of evidence".


Question 13 (c) (i)

Part (c) is assessing the student's knowledge of a core practical. The explanation of interference

patterns is well visited but this question considers only one part of the interference pattern when

the two slits are equidistant from the screen.

To explain the existence of a bright line requires three points to be made about each of: the path

difference, the phase difference and whether this is constructive or destructive interference.

In this case as the slits are equidistant from point 0 (as stated in the question), there is zero path

difference. Consideration of the path difference was often missing. Some students mentioned path

difference as a whole number of wavelengths which did not allow them to score the mark, as this

was not specific enough.

The waves are in phase at this point which gives constructive interference and hence a bright line.

MP2 and MP3 were more commonly seen.

This response scores 3 marks.

Superposition is accepted in place of interference,

but not superimposition.


A correct 3-mark answer.

MP1 line 1. This mark was least commonly

awarded as students did not mention path

difference.

MP2 line 2

MP3 line 3

Question 13 (c) (ii)

Drawing on knowledge that the path difference between the two waves is one whole wavelength

the only acceptable answer is 600 nm.


Question 14 (a) (iii)

This is a real image as it is formed on the other side of the lens to the object.

Most students realised that this was a real image. An explanation alluding to the rays passing

through the image was a common response although some found it difficult to express with clarity.

A perfect answer.

A common response was to state that "the image

was formed on the other side of the lens". This

does not make it clear that object and the image

are on different sides of the lens.


Question 14 (a) (i) - (ii)

It was encouraging to see that students generally used a ruler and sharp pencil to complete the ray

diagram. Those students who were unable to recall how to draw the paths of the rays were unlikely

to score well in the whole of this question totalling 5 marks.

Some students did not realise where the rays changed direction and drew rays that seemed to

change direction in random places.

Care needs to be taken in drawing the rays, using both a ruler and the lines on the graph paper as a

guide. A small inaccuracy on the left hand side of the diagram could lead to a larger inaccuracy in

locating the position of the image on the right hand side.


This response shows the paths of two rays

correctly drawn using a ruler with the image drawn

in the correct position. Three marks is scored in

part (a)(i).

In (a)(ii) the magnification is correctly calculated

using the ratio of the height of image to height of

object. Alternately a ratio of image distance to

object distance could be calculated.

Whilst the position of the image can be located by

drawing just two rays, it is good practice to add the

third ray because if the three rays do not all meet

in the same place, this can highlight when the path

of one ray has been incorrectly drawn.


Question 14 (b) (i)

The requirement in this question was for the description of a method. Therefore the emphasis

should be on measurements that need to be made. The focal length is the distance between the

lens and the position of the image formed from an object at infinity or (approximately) an object at

a large distant from the lens.

The image of a distant object can be projected on to a screen and the distance between the screen

and the image is measured. Alternatively, using parallel rays from a ray box, since rays from a

common point at infinity will be parallel when they are incident on the lens. The focal length is the

distance between the lens and the point at which the rays converge.

Correct description using parallel rays and a

correct measurement for the focal length has been

stated.

The focal length is the distance from lens to image.


Question 14 (b) (ii)

Rays of light are refracted on passing through a lens. The thicker lens will cause more refraction

and a shorter focal length as the rays of light converge at a point closer to the lens.

For MP1 correct reference to refraction was required. References to reflection or diffraction were

also seen and scored no mark.

For MP2 rays converge or meet at a point closer to the lens. It is incorrect here to state that the rays

meet at the focal point. This is only true if the rays arriving at the lens are parallel.

Correct reference to refraction for MP1. For MP2

the rays are meeting at a point closer to the lens.


Question 14 (b) (iii)

Students found this question challenging. The unfamiliar context required students to use their

knowledge of the magnification of a lens (m=v/u) as a starting point and use this to follow through a

logical argument to arrive at a conclusion.

Students answering this question most successfully started with the equation m=v/u . Firstly,

making the observation that photograph 2 is more magnified. Secondly, although this was not

commonly stated, establishing that u is the same in both photographs. Then it can be seen from

the equation that v must be larger. This then leads to a larger f from the thin lens formula arriving

at the 200 mm lens. This seemed counter intuitive to many. A significant number deduced that one

or either of the two lenses was more powerful and so produced a more magnified image. These

students were not distinguishing between situations involving near and far objects and were

probably thinking about the image produced by a magnifying glass.


A 5- mark answer. This student has stated relevent

equations and starting with a high magnification

has used the equations to follow through an

argument, leading to the correct conclusion.

MP1 lines 2 and 3.

MP2 lines 4 and 5.

MP3 line 4.

MP4 line 5.

MP5 correct conclusion in last 2 lines.


karen

karen

Delete space

Another 5-mark answer. In this response that

student has followed the argument in the reverse

order starting with the assumption that the focal

length increases and using the thin lens formula.

MP1 line 6.

MP2 line 5.

MP3 line 3

MP4 line 2.

MP5 last 2 lines.


This response scores 3 marks all in the first 3 lines.

The second half of the response is repeating what

has already been said but for the alternative lens.

The term "zooming in" was frequently seen. Whilst

a common photographic term, this is not a physics

term and so needed clarifying for MP1.


Question 15 (a)

In high intensity light the rate of incident photons is greater. Since one photon is absorbed by one

electron, more electrons are released every second. A greater rate of electrons pass through the

external circuit creating a larger current and the batteries charge more quickly.

Some key ideas of physics were being assessed in this question.

a higher intensity of light means the rate of incident photons is greater

one photon is absorbed by one electron

linking an increase in the rate of electrons with an increase in current


A good 4-mark answer.

Line 1: more photons per second for MP1.

Line 2: the idea of a one to one interaction

between photons and electrons for MP2.

Line 5: "more photoelectrons" also linked to an

increased rate from line 1 for MP3.

Line 6: more current.


MP1 and MP3 could not be awarded unless there was a clear reference to rate or number per unit

time. MP4 needed to refer to a quantity in the external circuit that was greater as a result.

Many students incorrectly referred to an increase in the energy of photons in high intensity light,

transferring a greater energy to the electrons, leading to an increased current.

Scores 4 marks.

MP1 lines 2 and 3

MP2 line 3

MP3 line 4

MP4 lines 5 and 6

A high intensity of light means that there are more

photons per second.

A large current means the rate of flow of electrons

is greater.


Question 15 (b)

To determine the energy generated the power must first be determined using P=I x A. The power

can then be substituted into E = P x t ensuring that the time (8 hours) is converted into seconds.

Use of the two relevent equations for intensity and power were often well done. Many students did

not multiply the energy by an efficiency of 23% limiting their score to two marks. This information is

within the passage (5th line).

MP1 top two lines of working, for using P = I x A,

arriving at P=26000 W

MP2 third line of working, for using E = P x t with

time converted to seconds, arriving at E = 7488 MJ

MP3 last line of working, multiplying by efficiency

of 23% to give correct final answer.


karen

karen

Insert space before =

karen

karen

Insert space before =

Highlight key points made in the passage to help

you remember that they are there as you answer

the questions.


Question 15 (c)

Using E = P x t with information given in the passage. There are four motors each with a power of

7.5 kW.

A correct 2-mark answer. The answer may be given

in any correct unit MJ, kJ, J.

Don't forget to convert kW to W, and time from

hours to seconds.


Question 15 (d)

Using change in gravitation potential energy = mass x g x change in height with information given in

the passage.

A correct answer.


Question 15 (e)

There needs to be an appreciation that, at night, the motors need to use as small amount as energy

as possible.

Air resistance is greater at faster speeds or, at lower heights where the air is more dense. With

more air resistance the motors would need to provide a greater forward force and therefore

require more energy. The plane flies at a lower speed at this lower height to conserve battery

energy.

A good 3-mark answer.


karen

karen

Change as to of

This is a well written answer scoring 2 marks. This

answer scores MP1 and MP3 but has not referred

to force from the motors to gain MP2.


Question 15 (f)

Many students referred to the idea that solar

planes would provide a "greener" or "more

environmentally friendly" method of flying. Use of

these terms do not generally gain credit as they

are vague terms showing little progress from

GCSE. The emphasis for this question is on the

advancement of the technology, not necessarily

linked solely to air travel.

In this response the mark is secured in the first five

words, as it conveys the advancement of

technology.


Scores one mark for the idea of advancing solar

technologies.

A good one mark answer.


Question 16 (a)

Using the information in the question it should be established that the resultant force F is equal to

0 as the balloon has reached a constant upwards speed and the vertical forces are balanced.

With F=0, to calculate the viscous drag force, the upthrust and weight need to be determined.

weight = (mass of balloon + helium) x g

upthrust = (density of air) x volume of balloon x g

The weight was commonly calculated correctly. Of those students who remembered how to

calculate upthrust, a common mistake was the recall of the volume of sphere, with the equation for

the area of a circle often seen.


A 4-mark answer.

Line 1: the student has written out the expression

for upthust with F=0 scoring MP1.

Line 2: the student has shown working for each of

the terms upthrust and weight. In this case it can

be assumed that the F corresponds to viscous drag

from their expression on the first line.

Line 3 and 4: substitution of correct values leading

to a correct answer.


This student has carried out the correct method

but has used an incorrect formula for the volume

of a sphere (on line 2) so cannot score MP3 and

MP4. This was a common mistake.

Learn the formula for the volume of a sphere.


This answer shows another common mistake. On

the second line they have attempted to calculate

the upthrust but have omitted g.


Question 16 (b)

There needed to be a link between viscosity and temperature. On a warmer day viscosity increases

creating a larger force opposing the motion of the balloon.

Scores one mark on the first line.


Paper SummaryThis paper provided candidates a wide scope in which to demonstrate their understanding of the

physics within the AS specification. Questions included both short and long written responses,

aswell as short and multi-step calculations.

Based upon the performance on this paper, students would benefit from:

memorising key mathematical formulae that are not provided on the paper, such as the volume

of a sphere

memorising definitions, for example in this paper, the definition of a real image and of a

wavefront.

learning to recognise and apply the relevent physics in unfamiliar situations

further practise at writing a coherent argument to form a logical conclusion

practise at evaluating practical investigations and calculations of uncertainties

practise at drawing a line of best fit on a graph of real data to give an even spread of points either

side of the line.


karen

karen

as well

karen

karen

practice

Grade BoundariesGrade boundaries for this, and all other papers, can be found on the website on this link:

http://www.edexcel.com/iwantto/Pages/grade-boundaries.aspx


http://www.edexcel.com/iwantto/Pages/grade-boundaries.aspx

Pearson Education Limited. Registered company number 872828

with its registered office at 80 Strand, London WC2R 0RL.

Powered by TCPDF (www.tcpdf.org)

http://www.tcpdf.org

gce physics 8ph0 02 - revisely

Documents